1. Field of the Invention
This invention relates to re-entrant geometry gate electrodes for integrated circuit structures and the formation of same. More particularly this invention relates to re-entrant geometry gate electrodes formed by selective implantation of a semiconductor material prior to etching the semiconductor material to form the re-entrant gate electrode structure.
2. Description of the Related Art
Implantation of atoms, such as, for example a dopant, into a crystalline structure, such as a single crystal silicon substrate or an epitaxial layer, or a polycrystalline structure such as polysilicon, disrupts the crystalline structure of the material being implanted. The local level of damage to the crystalline structure continues to increase during the implantation until destruction or disappearance of local order is completes, i.e., all crystallinity is gone and an amorphous state, e.g., of silicon, exists in that implanted region of the structure. Normally the disrupted crystalline structure is then subjected to an anneal which restores the crystalline structure to its previous form, i.e., remedies the damage done to the particular crystalline structure.
However, if the damaged crystalline structure is etched after such an implantation, without an intervening anneal step, the etching step is found to be non-uniform, with the portion of the crystalline structure damaged by the previous implantation step responding to the etch treatment at an accelerated rate, i.e., the damaged portion of the crystalline structure etches at a faster rate. This exhibited selectivity is believed to be because many of the atomic bonds have been broken during the implantation in the implanted region of the substrate, thus allowing bonding to plasma species to occur more readily than in regions where, for example, the silicon--silicon bonds first must be broken before additional reaction occurs. Normally this is not a desirable feature and is avoided by first annealing the damaged structure prior to the etching step.